Plasma Energy Density Research Articles

Hybrid GRMHD and force-free simulations of black hole accretion

ABSTRACT We present a new approach for stably evolving general relativistic magnetohydrodynamic (GRMHD) simulations in regions where the magnetization $\sigma =b^2/\rho c^2$ becomes large. GRMHD codes typically struggle to evolve plasma above $\sigma \approx 100$ in simulations of black hole accretion. To ensure stability, GRMHD codes will inject mass density artificially to the simulation as necessary to keep the magnetization below a ceiling value $\sigma _{\rm max}$. We propose an alternative approach where the simulation transitions to solving the equations of general relativistic force-free electrodynamics (GRFFE) above a magnetization $\sigma _{\rm trans}$. We augment the GRFFE equations in the highly magnetized region with approximate equations to evolve the decoupled field-parallel velocity and plasma energy density. Our hybrid scheme is explicit and easily added to the framework of standard-volume GRMHD codes. We present a variety of tests of our method, implemented in the GRMHD code koral, and we show results from a 3D hybrid GRMHD + GRFFE simulation of a magnetically arrested disc (MAD) around a spinning black hole. Our hybrid MAD simulation closely matches the average properties of a standard GRMHD MAD simulation with the same initial conditions in low magnetization regions, but it achieves a magnetization $\sigma \approx 10^6$ in the evacuated jet funnel. We present simulated horizon-scale images of both simulations at 230 GHz with the black hole mass and accretion rate matched to M87*. Images from the hybrid simulation are less affected by the choice of magnetization cut-off $\sigma _{\rm cut}$ imposed in radiative transfer than images from the standard GRMHD simulation.

Optimization of Surface Finish of Plasma Metal Deposited Stainless Steel 316L Parts by Utilization of Plasma Beam Remelting (PBR) and Taguchi Methodology

The study aimed to optimize the Plasma Beam Polishing process for 316L stainless steel components to reduce anisotropy and poor surface roughness using statistical analysis. An experimental design investigated the impacts of managing factors on surface roughness, with scanning speed having the ultimate impact, followed by beam power and energy density. For lower values of plasma energy density and scanning speed, and a focal location without changes on the metal surface, there was a strong tendency for the estimated Ra to drop with increasing laser power. The process parameters were changed throughout a broad range of values, making it challenging to model the dependent variable across the whole range of experimental trials. The study supports the potential of PBP as a post-processing method for additive manufacturing components.

Recent results on high-β plasma confinement studies in the Gas Dynamic Trap

This paper is devoted to experimental studies of plasma confinement with high relative pressure ( $\beta$ ) in the Gas Dynamic Trap (BINP, Novosibirsk). In previous high- $\beta$ confinement studies a maximum local $\beta = 0.6$ was achieved in the fast-ion turning point, contributed to by a beam-driven population of fast ions with an anisotropic distribution function. In this study the axial magnetic field profile was modified to bring the turning points closer to one another, which effectively increased the energy density of plasma and pushed the $\beta$ value higher. Experiments were performed for two non-standard magnetic configurations, where the axial fast-ion confinement region length was reduced by 1.5 and 2 times compared with the standard configuration. The average values of $\langle \beta _{\perp } \rangle$ over the plasma central cross-section were found to be 0.1 and 0.18, respectively, for the two configurations, with the latter value significantly exceeding the $\langle \beta _{\perp } \rangle =0.08$ of the standard configuration, in which the previous record was set. Moreover, halving the fast ion confinement region almost doubled the D–D fusion proton flux from the trap centre compared with the standard configuration. The electron temperature in both new magnetic configurations was only slightly smaller than in the standard configuration. In addition, an effect of Alfvén ion–cyclotron instability (AICI) development on the pressure in the turning points is discussed. Presumably, with some decrease in magnetic field an evolving AICI does not result in considerable pressure axial redistribution, so the pressure maximum is in the turning points’ vicinity despite the instability.

Simulations on Synchrotron Radiation Intensity and Rotation Measure of Relativistic Magnetized Jet PKS 1502+106

Strong γ-ray outbursts have been observed to emanate from PKS 1502+106, followed by highly variable fluxes in radio, visual, ultraviolet and X-ray bands. Numerical simulations have been conducted to relate the observations to potential theoretical models. The plasma attributes, such as mass density, plasma flow velocity and energy density, cannot be directly observed. However, the Stokes parameters of synchrotron radiation from the plasma can be measured to deduce the plasma attributes. Many studies have been conducted on synchrotron radiation intensity, with only a few on the rotation measure (RM) related to Faraday rotation. In this work, overpressured relativistic magnetized axisymmetric jets are simulated to acquire the synchrotron radiation maps, incorporating Faraday rotation, of the widely discussed jet, PKS 1502+106. The intensity maps and RM maps of the PKS 1502+106 are simulated under practical constraints, and compared with the available observation data to explore specific features of the jet. The simulated intensity maps match well with the observation data in size and shape. The observed spine–sheath polarization structure, sign change in the RM slice and opposite RM gradients have been reproduced. The conjecture of helical magnetic field morphology in the literature has also been validated by comparing the simulation results under different magnetic field morphologies.

Energy Partition of Thermal and Nonthermal Particles in Magnetic Reconnection

Magnetic reconnection has long been known to be the most important mechanism for quick conversion of magnetic field energy into plasma kinetic energy. In addition, energy dissipation by reconnection has gained attention not only as a plasma heating mechanism, but also as a plasma mechanism for accelerating nonthermal particles. However, the energy partitioning of thermal and nonthermal plasmas during magnetic reconnection is not understood. Here, we studied energy partition as a function of plasma sheet temperature and guide magnetic field. In relativistic reconnection with an antiparallel magnetic field or a weak guide magnetic field, it was found that the nonthermal energy density can occupy more than 90% of the total kinetic plasma energy density, but strengthening the guide magnetic field suppresses the efficiency of the nonthermal particle acceleration. In nonrelativistic reconnection for an antiparallel magnetic field, most dissipated magnetic field energy is converted into thermal plasma heating. For a weak guide magnetic field with a moderate value, however, the nonthermal particle acceleration efficiency was enhanced, but strengthening the guide field beyond the moderate value suppresses the efficiency.

Dependency of Argon Chromium Plasma Coefficients on Power in Magnetron Sputtering

In this paper, we have studied Cr–Ar plasma in low pressure at 3 mTorr at different powers (40–140) W experimentally and theoretically. We have measured parameters of the plasma (density of plasma, ionic density, electronic temperature, and electron energy density function EEDF) using Langmuir probe. The other parameters which could not measure such as electronic mobility, drift velocity, average electron energy and diffusion coefficients are calculated. The aim of this study is to be determined the Cr–Ar plasma parameters that are necessary for preparing thin films at different powers. We have used SEM and XRD to study the morphology of these films.

Toluene Decomposition by Non-Thermal Plasma Assisted 2d Coox/Al2o3: The Relative Contributions of Specific Energy Density of Plasma, Co 3+ and Oxygen Vacancy

Toluene Decomposition by Non-Thermal Plasma Assisted 2d Coox/Al2o3: The Relative Contributions of Specific Energy Density of Plasma, Co 3+ and Oxygen Vacancy

Statistical Characterization of the Dynamic Near‐Earth Plasma Sheet Relative to Ultra‐Low Frequency (ULF) Wave Growth at Substorm Onset

AbstractMagnetospheric substorms are a complex phenomenon. During the initial stages of a substorm a variety of important processes occur in near‐Earth space within a span of several minutes. The relative timing and links between these processes are critical to understanding how, where and when substorms may occur. One of the first observed signatures at substorm onset is the exponential increase in ULF (Ultra‐Low Frequency) wave power in the near‐Earth magnetotail (e.g., −7.5 ≤ XGSM ≤ −12.5 RE). We use the Time History of Events and Macroscale Interactions during Substorms spacecraft to examine the conditions in the magnetotail plasma sheet before, during and after local ULF wave growth. Prior to the ULF wave growth, the magnetotail stretches with convectional flows dominating. We then find strong earthward and azimuthal flows that peak at a similar time to the peak ULF wave power. These flows are found to be faster in the mid‐tail (−10 ≤ XGSM ≤ −12.5 RE) than the near‐tail (−7.5 ≤ XGSM ≤ −10 RE). Examining the local plasma energy density (magnetic, thermal and kinetic), we find no statistical decrease that could explain the exponentially growing ULF waves, in fact the local energy density is found to increase. This suggests that there may be an injection of energy from elsewhere in the magnetotail. Following the peak ULF wave power the tail is seen to dipolarize, and the local energy density is enhanced.

The guiding effect of artificially injected gas bubble on the underwater pulsed spark discharge and its electrical and acoustic parameters after breakdown

The presence of a low density area is beneficial to the facilitation of the underwater pulsed spark discharge, which can be achieved by artificially injecting gas bubble in between the inter-electrode gap. The generation of intensive acoustic waves by such gas-bubble-guided spark discharges makes them promising underwater acoustic sources in multiple practical applications. This paper is aimed at comprehensive investigation of the guiding effect of the injected bubble on the pre-breakdown process of underwater pulsed spark discharges and potential correlations between their subsequent electrical and acoustic parameters with the purpose of optimizing the acoustic emission. The breakdown probability and the pre-breakdown delay were used to evaluate the general facilitation effect brought by the injected bubble. Experimental and numerical works have been conducted and allow observation on the dynamics of the injected bubble under the influence of the applied voltage. Different guiding modes of the injected bubble for plasma streamers' propagation have been observed regarding its relative position. The characteristics of the electrical properties of gas-bubble-guided spark discharges, including the plasma resistance and the plasma energy density, were analyzed by relating them with the breakdown voltage. The dependency of the acoustic wave amplitude and the acoustic efficiency on these electrical parameters was verified, which provides solid regulation principles for the optimization of the plasma-acoustic system for target practical applications.

Penetration of plasma jet into porous dielectric layer: confirmed by surface charge dissipation of silicone rubber

The penetration of plasma in the porous structure is important for its application in plasma catalysis, plasma medicine, etc. In this paper, the penetration of plasma species in the porous kaolin layer was investigated. The silicone rubber was chosen as a probe and the inorganic porous dielectric layer was constructed with granular kaolin coated on the surface of silicone rubber. AC and pulsed plasma jets were applied to the silicone rubber, and the surface charge dissipation of bulk silicone rubber was measured to characterize the changes of surface property caused by the plasma penetration. The results showed that plasma could penetrate the porous dielectric layer on the silicone rubber and interact with the surface of silicone rubber, thus accelerating the surface charge dissipation of the bulk silicone rubber. The increase of shallow traps and surface conductivity after plasma treatment was the main reason for the acceleration of surface charge dissipation. The surface charge dissipation is enhanced with the increase of treatment time and the generating voltage of plasma. The surface charge dissipation declined for silicone rubber with a thicker kaolin layer due to the blocking of the kaolin layer on the interaction of plasma and the silicone rubber. For the same kind of plasma, the charge dissipation rate was linearly related to plasma dose which was represented by the energy density of plasma applied on the coated silicone rubber. At the same energy density, the surface charge dissipation of silicone rubber after pulsed plasma treatment was faster than that of AC plasma.

Pair-regulated Klein–Nishina relativistic magnetic reconnection with applications to blazars and accreting black holes

ABSTRACT Relativistic magnetic reconnection is a powerful agent through which magnetic energy can be tapped in astrophysics, energizing particles that then produce observed radiation. In some systems, the highest energy photons come from particles Comptonizing an ambient radiation bath supplied by an external source. If the emitting particle energies are high enough, this inverse Compton (IC) scattering enters the Klein–Nishina regime, which differs from the low-energy Thomson IC limit in two significant ways. First, radiative losses become inherently discrete, with particles delivering an order-unity fraction of their energies to single photons. Secondly, Comptonized photons may pair produce with the ambient radiation, opening up another channel for radiative feedback on magnetic reconnection. We analytically study externally illuminated highly magnetized reconnecting systems for which both of these effects are important. We identify a universal (initial magnetization-independent) quasi-steady state in which gamma-rays emitted from the reconnection layer are absorbed in the upstream region, and the resulting hot pairs dominate the energy density of the inflow plasma. However, a true pair cascade is unlikely, and the number density of created pairs remains subdominant to that of the original plasma for a wide parameter range. Future particle-in-cell simulation studies may test various aspects. Pair-regulated Klein–Nishina reconnection may explain steep spectra (quiescent and flaring) from flat-spectrum radio quasars and black hole accretion disc coronae.

Hadronic effects on charmonium elliptic flows in heavy-ion collisions

Transport and Langevin equations are employed to study hadronic medium effects on charmonium elliptic flows in heavy-ion collisions. In Pb-Pb collisions, the anisotropic energy density of the quark-gluon plasma (QGP) in the transverse plane is transformed into hadron momentum anisotropy after the phase transition. Charmonia with high transverse momentum $p_T$ are produced via the primordial hard process and undergo different degrees of dissociation along different paths in the QGP. They then scatter with light hadrons in the hadron phase. Both contributions to the charmonium elliptic flows are studied at moderate and high transverse momenta. The elliptic flows of the prompt $J/\psi$ are found to be considerably enhanced at high transverse momentum when the charmonium diffusion coefficients in the hadronic medium are parametrized through the geometry scale approximation. This hadronic medium effect is negligible for quarkonia with larger mass such as bottomonia.

Research on Material Removal Mechanism of Micro-EDM in Deionized Water

As one of the most promising processing methods, the microelectrical discharge machining (micro-EDM) process is widely used in industrial production; however, the material removal mechanism of micro-EDM in deionized water has not been clarified due to scale effect. In this paper, the influence of discharge parameters on the discharge crater size was studied by means of a single-pulse discharge experiment using a resistor–capacitor circuit (RC circuit). The variation trend of the discharge crater size with open-circuit voltage and capacitance was discussed based on the experimental results. The results show that the diameter and depth of the discharge crater increases with capacitance and open-circuit voltage due to the increasing discharge duration and the energy density of the discharge plasma. The discharge energy increases with the increase of capacitance and open-circuit voltage, which causes more materials to melt and vaporize, leading to the crater volume becoming larger. This study has reference value for the further application of micro-EDM adopting deionized water as a dielectric.

PARAMETERS OF HYDROGEN PLASMA STREAMS IN QSPA-M AND THEIR DEPENDENCE ON EXTERNAL MAGNETIC FIELD

Present experimental studies are aimed at analysis of hydrogen plasma stream parameters in various working regimes of QSPA-M operation. Temporal distributions of plasma electron density are reconstructed with optical emission spectroscopy. The magnetic field influence on plasma streams parameters is analyzed. It is shown that in regimes with additional magnetic field the plasma electron density increases by an order of magnitude in comparison with a density value without magnetic field. The plasma velocity and energy density parameters as well as their temporal behaviors were estimatedin different operating regimes of QSPA-M facility. Features of plasma visible radiation were analyzed. This information is important for QSPA-M applications in experiments on interaction of powerful plasma streams with material surfaces.

Effect of sliding discharge on proliferation and death of brain microvessel endothelial cells in vitro

The dose-dependent effects of plasma exposure to a unipolar nanosecond sliding discharge over the surface of the culture medium in a closed plate on the cells of cerebral endothelium in vitro were studied. Using a 24-well plate, the surface plasma energy density of one pulse was 360 μJ/cm2 at a pulse frequency of 100 Hz. It has been shown that in the creeping discharge plasma there is an active excitation of air molecules, the formation of positive nitrogen and oxygen ions, and the formation of carbon monoxide. In the dose density range of 0-32 J/cm2, the dose-dependent effects were assessed in the 4-12 h post-radiation period. Cell death was analyzed with an assessment of the total number of cells, necrotic cells, cells in apoptosis (phosphatidylserine externalization, internucleosomal DNA fragmentation) and their proliferative activity (Ki67-immunopositive cells). A preliminary assessment of subtle dose-dependent effects indicates the peculiarities of the effect of small doses.

TJ cm−3 high energy density plasma formation from intense laser-irradiated foam targets composed of disordered carbon nanowires

High energy density plasma formation from intense laser-irradiated foam targets composed of disordered carbon nanowires is investigated using three-dimensional particle-in-cell simulations. It is shown that due to the unprecedentedly high laser energy absorption rate of the foam target, approximately three times larger as compared with simple solid targets, the plasma energy density reaches an unexplored TJ cm−3 regime at 1023 W cm−2 laser irradiation. In addition, nanowire thermal expansion caused by prepulse heating is considered. We find that after expansion, the target becomes relativistically transparent to the main pulse. The average value of particle energy density decreases slightly and its distribution tends to resemble that of solid targets. Furthermore, energy density scaling with laser intensities is given. It suggests that an even more extreme plasma state is reachable using ultraintense lasers, as the energy loss to photons caused by quantum electrodynamics effects is rather negligible.

Numerical simulations of gravitational waves from early-universe turbulence

We perform direct numerical simulations of magnetohydrodynamic turbulence in the early universe and numerically compute the resulting stochastic background of gravitational waves and relic magnetic fields. These simulations do not make the simplifying assumptions of earlier analytic work. If the turbulence is assumed to have an energy-carrying scale that is about a hundredth of the Hubble radius at the time of generation, as expected in a first-order phase transition, the peak of gravitational wave power will be in the mHz frequency range for a signal produced at the electroweak scale. The efficiency of gravitational wave (GW) production varies significantly with how the turbulence is driven. Detectability of turbulence at the electroweak scale by the planned Laser Interferometer Space Antenna (LISA) requires anywhere from 0.1% to 10% of the thermal plasma energy density to be in plasma motions or magnetic fields, depending on the model of the driving process. Our results predict a new universal form below the spectral peak frequency that is shallower than previously thought. This implies larger values of the GW energy spectra in the low-frequency range. This extends the range where turbulence is detectable with LISA to lower frequencies, corresponding to higher energy scales than the assumed energy-carrying scale.

Plasma characteristics of a tapered coaxial gun and its damage effect on tungsten target

• A tapered coaxial plasma gun with negative pulse was used to obtain more suitable plasma parameters for simulation of the Type- I ELM in tokamak. • The plasma parameters of the tapered coaxial gun were measured. The characteristics of plasma are analyzed. • Fusion plasma surface interactions relevant results were provided. Damage effect on target was analyzed. Due to the property of high energy density, temperature and density, the plasma prodced by the coaxial gun is usually untilized to simulate the Type- I ELM in tokamak. In this work, the plasma characteristics of a tapered coaxial gun was studied and its effect on the tungsten target was investigated. By using current probe, photodetector, spectrometer and calorimeter, it is found that the plasma energy density, density and velocity increase obviously with the discharge voltage. The maximum energy density could reach 1.4 MJ/m 2 , the maximum electron density could reach 3 × 10 15 /cm 3 , and the maximum ion kinetic energy could reach 113 eV at the voltage of 16 kV, which is suitable for simulating the type I Elms in Tokamak. After one shot, there are many cracks and ablative spots on the surface of W target. Whose size could reach ∼ μm by scanning electron microscope(SEM), this is because W material will become brittle after the frequent heating and cooling alternations under thermal shock and the melt motion driven by high plasma pressure gradient. With the Energy Dispersive Spectrometer(EDS), it can be seen that no matter from the cracks and other area of the surface after one shot, the impurity can be ignored. These results help us to better understand the damage effect of tungsten target for further research.

Generation and Diagnostics of Pulse Plasma Flows

Pulsed plasma accelerators are widely used for the production of high-temperature pulsed plasma flows for fundamental and practical applications. The basic parameters of pulsed plasma accelerators are the characteristics of the external electric and magnetic circuits, as well as the structural and energy properties of the plasma flow. This work aims to characterize an IPU-30 pulsed plasma accelerator. The triple Langmuir probe method, calorimetric plasma energy density measurements, Rogowski coil, and high-speed visible imaging with a Phantom VEO710S fast camera are used to diagnose the pulsed plasma obtained in the IPU-30. The local plasma parameters such as electron temperature and density, the energy density of the pulsed plasma flow, pulsed plasma current, and also discharge current are experimentally obtained at different discharge voltages and air pressure in the chamber. The typical waveforms of the triple probe and Rogowski coil are presented in the form of oscillograms. The images of plasma formation in the discharge gap are obtained and the velocity of a pulsed plasma flow is measured.

An Investigation on the Application of Plasma-Activated Gas to Laminar Lifted Nonpremixed Jet Flames

This paper is to experimentally investigate the effect of plasma-activated gas on the characteristics of a laminar lifted nonpremixed jet flame in a coflow stream. A coaxial dielectric-barrier discharge is employed to activate fuel (C3H8) and oxidizer, respectively. It is shown that an enhancement of 12% and 50% in the liftoff velocity is observed for oxidizer and fuel activation, respectively. With the addition of O3 (1650 ppm) by oxidizer activation, the flame liftoff height is continuously decreased and the blowout velocity is extended. In contrast, a larger liftoff height, accompanied with a smaller blowout velocity, exhibits for flames with fuel activation. The inconsistent effect of fuel activation on the flame liftoff is presumably a contribution of the gas expansion, the conversion rate, and the corresponding product selectivity. The gas expansion is due to the fuel activation that produces lighter hydrocarbons than propane. The conversion rate and the H2 and CH4 selectivities are found to be associated with the plasma energy density. The flame propagation can be greatly enhanced to produce a nozzle-attached flame when the plasma energy density is high enough to effectively decompose C3H8 into H2. Nevertheless, a decrease in plasma energy is more sufficient for the cleavage of C–C bonds, resulting in a significant decrease in H2 selectivity, but a nearly unaltered CH4 selectivity. The reduced conversion due to the lower plasma energy, along with the gas expansion, produces a lifted flame with a larger liftoff height than the nonactivated flame.